DC-DC Converter

Abstract

Suppresses bias in voltage burden. [Solution] A DC-DC converter (1) comprises a transformer (Tr) in which a first winding connected to each of the AC side terminal pairs of a plurality of AC-DC conversion circuits (11, 12) constituting a first AC-DC conversion circuit group (10) and a second winding connected to each of the AC side terminal pairs of AC-DC conversion circuits (21, 22) constituting a second AC-DC conversion circuit group (20) are wound commonly around a core, and DC side terminal pairs for inputting and outputting DC power of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group are connected in series.

Description

[Technical field]

[0001] The present invention relates to a DC-DC converter. [Background technology]

[0002] A technology has been proposed for DC-DC converters capable of bidirectional DC power transfer, in which the input and output terminals of multiple isolated DC-DC converter units are connected in series to support higher voltages. Here, the isolated DC-DC converter unit is configured with a primary side AC / DC conversion circuit and a secondary side AC / DC conversion circuit connected via a transformer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-028333 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional technology, if there is an unintended variation in the circuit constants or control parameters of each AC / DC conversion circuit, the voltage borne by each unit may be biased, which may lead to damage to elements in the AC / DC conversion circuit. Therefore, in order to balance the voltage borne by each unit, it is necessary to perform complex control according to the operating conditions of the DC-DC converter. One aspect of the present disclosure aims to realize a series-connected DC-DC converter that can suppress the bias in voltage burden without performing complex control. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, one aspect of the present disclosure is a DC-DC converter including a first terminal pair and a second terminal pair, and controlling a transfer of power between the first terminal pair and the second terminal pair, the DC-DC converter including a first AC-DC conversion circuit group including a plurality of AC-DC conversion circuits, each of which is made up of a smoothing circuit and an active bridge circuit connected in cascade from the first terminal pair side, and is provided with an AC side terminal pair connected to the active bridge circuit for inputting and outputting AC power; a first winding connected to the AC side terminal pair of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, and a first winding connected to the AC side terminal pair of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, each of which is made up of a smoothing circuit and an active bridge circuit connected in cascade from the second terminal pair side. the first AC / DC conversion circuit group and the second AC / DC conversion circuit group are provided with an AC side terminal pair for inputting and outputting AC power connected to the active bridge circuit, a second winding connected to the AC side terminal pair of each of the AC / DC conversion circuits constituting the second AC / DC conversion circuit group, a core, and a control unit that controls switching elements included in the first AC / DC conversion circuit group, wherein the DC side terminal pairs for inputting and outputting DC power of the AC / DC conversion circuits constituting the first AC / DC conversion circuit group are connected in series between the first terminal pair, and a transformer is constituted in which the first winding and the second winding are commonly wound around the core. Effect of the Invention

[0006] According to one aspect of the present disclosure, it is possible to realize a series-connected DC-DC converter that can suppress bias in voltage burden without performing complex control. [Brief description of the drawings]

[0007] [Figure 1] 1 is a circuit diagram of a DC-DC converter according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram showing an overview of a transformer applied to the above-mentioned DC-DC converter. [Diagram 3] 4 is a circuit diagram showing an equivalent circuit of a conversion unit including a transformer of the DC-DC converter. FIG. [Figure 4] 3 is a waveform diagram showing currents and voltages at various points in the DC-DC converter when power transfer is zero. [Diagram 5] FIG. 2 is a circuit diagram of a DC-DC converter according to a first comparative example. [Figure 6] 1 is a graph showing the balance of DC voltages in each AC / DC conversion circuit in the DC-DC converter of Comparative Example 1, showing the transition at the start of a switching operation. [Figure 7] 4 is a graph showing the balance of DC voltages in each AC / DC conversion circuit in the DC-DC converter according to the first embodiment of the present disclosure, showing the transition at the start of a switching operation. [Figure 8] 4 is a diagram for explaining a path of a compensation current that flows when a difference in DC voltage occurs between AC / DC conversion circuits on the first DC power source side in the DC-DC converter according to the first embodiment of the present disclosure. FIG. [Figure 9] FIG. 11 is a circuit diagram of a DC-DC converter according to a second embodiment of the present disclosure. [Figure 10] FIG. 11 is a diagram for comparing a DC-DC converter according to embodiment 2 of the present disclosure with a DC-DC converter of comparative example 2, showing the balance between the DC voltage of the AC-DC conversion circuit on the first DC power source side and the DC current of the AC-DC conversion circuit on the second DC power source side. [Figure 11] FIG. 11 is a circuit diagram of a DC-DC converter according to a third embodiment of the present disclosure. [Figure 12] FIG. 11 is a diagram for comparing a DC-DC converter according to embodiment 3 of the present disclosure with a DC-DC converter of comparative example 3, showing the balance between the DC current of the AC-DC conversion circuit on the first DC power source side and the DC voltage of the AC-DC conversion circuit on the second DC power source side. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Embodiment 1] Hereinafter, embodiments according to one aspect of the present disclosure will be described with reference to the drawings. In the following description, the term "terminal" is used to mean a connection point of a specific circuit element inside an electric circuit, and does not necessarily mean that an external connection terminal such as a connector is provided.

[0009] <Configuration Overview of DC-DC Converter 1> FIG. 1 is a circuit diagram of a DC-DC converter 1 according to Embodiment 1. The DC-DC converter 1 is a bidirectional DC-DC converter capable of bidirectional power transfer between a first DC voltage source 91 and a second DC voltage source 92.

[0010] The first DC voltage source 91 is connected to the first terminal pair of the DC-DC converter 1, and the second DC voltage source 92 is connected to the second terminal pair of the DC-DC converter 1. The first terminal pair is composed of a high-potential side terminal u1 and a low-potential side terminal v1. The second terminal pair is composed of a high-potential side terminal u2 and a low-potential side terminal v2.

[0011] The DC-DC converter 1 includes a first AC-DC conversion circuit group 10, a second AC-DC conversion circuit group 20, a conversion unit 30, and a control device 40 (control unit). The first AC-DC conversion circuit group 10 is composed of a plurality of AC-DC conversion circuits. The second AC-DC conversion circuit group 20 is composed of at least one AC-DC conversion circuit.

[0012] In Embodiment 1, as a specific example, the first AC-DC conversion circuit group 10 is composed of two AC-DC conversion circuits, a first AC-DC conversion circuit 11 and a second AC-DC conversion circuit 12. Each of the first AC-DC conversion circuit 11 and the second AC-DC conversion circuit 12 has a DC side terminal pair for inputting and outputting DC power and an AC side terminal pair for inputting and outputting AC power.

[0013] The DC side terminal pair of the first AC / DC conversion circuit 11 is composed of a high potential side terminal u11 and a low potential side terminal v11. The AC side terminal pair of the first AC / DC conversion circuit 11 is composed of a terminal x11 and a terminal y11. The DC side terminal pair of the second AC / DC conversion circuit 12 is composed of a high potential side terminal u12 and a low potential side terminal v12. The AC side terminal pair of the second AC / DC conversion circuit 12 is composed of a terminal x12 and a terminal y12.

[0014] The DC side terminal pairs of the multiple AC / DC conversion circuits constituting the first AC / DC conversion circuit group 10 are connected in series between the first terminal pair (terminal u1 and terminal v1). That is, the high potential side terminal u1 of the first terminal pair is electrically common to the high potential side terminal u11 of the DC side terminal pair of the first AC / DC conversion circuit 11, and the low potential side terminal v1 of the first terminal pair is electrically common to the low potential side terminal v12 of the DC side terminal pair of the second AC / DC conversion circuit 12. The low potential side terminal v11 of the DC side terminal pair of the first AC / DC conversion circuit 11 and the high potential side terminal u12 of the DC side terminal pair of the second AC / DC conversion circuit 12 are connected to each other.

[0015] Therefore, in the first AC / DC conversion circuit group 10, the power supply voltage Vin (voltage between terminals u1 and v1) of the first DC voltage source 91 is shared between the first AC / DC conversion circuit 11 and the second AC / DC conversion circuit 12. In other words, the sum of the DC voltage Vdc11 between the DC side terminal pair (terminals u11 and v11) of the first AC / DC conversion circuit 11 and the DC voltage Vdc12 between the DC side terminal pair (terminals u12 and v12) of the second AC / DC conversion circuit 12 is equal to the power supply voltage Vin of the first DC voltage source 91.

[0016] In addition, in the first embodiment, as a specific example, the second AC / DC conversion circuit group 20 is composed of two AC / DC conversion circuits, a third AC / DC conversion circuit 21 and a fourth AC / DC conversion circuit 22. Each of the third AC / DC conversion circuit 21 and the fourth AC / DC conversion circuit 22 has a DC side terminal pair for inputting and outputting DC power and an AC side terminal pair for inputting and outputting AC power.

[0017] The DC side terminal pair of the third AC / DC conversion circuit 21 is composed of a high potential side terminal u21 and a low potential side terminal v21. The AC side terminal pair of the third AC / DC conversion circuit 21 is composed of a terminal x21 and a terminal y21. The DC side terminal pair of the fourth AC / DC conversion circuit 22 is composed of a high potential side terminal u22 and a low potential side terminal v22. The AC side terminal pair of the fourth AC / DC conversion circuit 22 is composed of a terminal x22 and a terminal y22.

[0018] The DC side terminal pairs of the multiple AC / DC conversion circuits constituting the second AC / DC conversion circuit group 20 are connected in series between the second terminal pair (terminal u2 and terminal v2). That is, the high potential side terminal u2 of the second terminal pair is electrically common to the high potential side terminal u21 of the DC side terminal pair of the third AC / DC conversion circuit 21, and the low potential side terminal v2 of the second terminal pair is electrically common to the low potential side terminal v22 of the DC side terminal pair of the fourth AC / DC conversion circuit 22. The low potential side terminal v21 of the DC side terminal pair of the third AC / DC conversion circuit 21 and the high potential side terminal u22 of the DC side terminal pair of the fourth AC / DC conversion circuit 22 are connected to each other.

[0019] Therefore, in the second AC / DC conversion circuit group 20, the power supply voltage Vout (voltage between terminal u2 and terminal v2) of the second DC voltage source 92 is shared between the third AC / DC conversion circuit 21 and the fourth AC / DC conversion circuit 22. In other words, the sum of the DC voltage Vdc21 between the DC side terminal pair (terminal u21 and terminal v21) of the third AC / DC conversion circuit 21 and the DC voltage Vdc22 between the DC side terminal pair (terminal u22 and terminal v22) of the fourth AC / DC conversion circuit 22 is equal to the power supply voltage Vout of the second DC voltage source 92.

[0020] For convenience, the power supply voltage of first DC voltage source 91 is suffixed with "in" and the power supply voltage of second DC voltage source 92 is suffixed with "out". As described above, DC-DC converter 1 is capable of bidirectional power transfer, and the direction of power transfer is not limited to the one direction from first DC voltage source 91 to second DC voltage source 92.

[0021] <Configuration of AC / DC conversion circuit> The first AC / DC conversion circuit 11 and the second AC / DC conversion circuit 12 constituting the first AC / DC conversion circuit group 10 each include a smoothing circuit and an active bridge circuit connected in cascade from the first terminal pair (terminal u1 and terminal v1) side. Each is also provided with an AC side terminal pair for inputting and outputting AC power connected to the respective active bridge circuit.

[0022] The first AC / DC conversion circuit 11 has a smoothing circuit 111, an active bridge circuit 112, and an AC side terminal pair (terminal x11 and terminal y11) for inputting and outputting AC power connected to the active bridge circuit 112. The smoothing circuit 111 may be any circuit that smoothes the voltage between the DC side terminal pair (terminal u11 and terminal v11), and is configured to include a capacitor C11 provided between the terminal u11 and the terminal v11.

[0023] The active bridge circuit 112 includes two legs connected in parallel to a DC side terminal pair (terminal u11 and terminal v11). One leg is configured by connecting a switching element S11 and a switching element S21 in series, and the connection point between them is one terminal x11 of the AC side terminal pair. The other leg is configured by connecting a switching element S31 and a switching element S41 in series, and the connection point between them is the other terminal y11 of the AC side terminal pair.

[0024] The second AC / DC conversion circuit 12 has a similar configuration to the first AC / DC conversion circuit 11. Each part in the second AC / DC conversion circuit 12 has the same name as the corresponding part in the first AC / DC conversion circuit 11, with the last 1 in the reference numerals indicating each part changed to 2.

[0025] The third AC / DC conversion circuit 21 and the fourth AC / DC conversion circuit 22 constituting the second AC / DC conversion circuit group 20 each include a smoothing circuit and an active bridge circuit connected in cascade from the second terminal pair (terminal u2 and terminal v2) side. Each of them also includes an AC side terminal pair connected to the active bridge circuit for inputting and outputting AC power.

[0026] The third AC / DC conversion circuit 21 has a smoothing circuit 211, an active bridge circuit 212, and an AC side terminal pair (terminal x21 and terminal y21) for inputting and outputting AC power connected to the active bridge circuit 212. The smoothing circuit 211 may be any circuit that smoothes the voltage between the DC side terminal pair (terminal u21 and terminal v21), and is configured to include a capacitor C21 provided between the terminal u21 and the terminal v21.

[0027] The active bridge circuit 212 includes two legs connected in parallel to a DC side terminal pair (terminal u21 and terminal v21). One leg is configured by connecting a switching element S51 and a switching element S61 in series, and the connection point between them is one terminal x21 of the AC side terminal pair. The other leg is configured by connecting a switching element S71 and a switching element S81 in series, and the connection point between them is the other terminal y21 of the AC side terminal pair.

[0028] The fourth AC / DC conversion circuit 22 has a similar configuration to the third AC / DC conversion circuit 21. Each part in the fourth AC / DC conversion circuit 22 has the same name as the corresponding part in the third AC / DC conversion circuit 21, with the last 1 in the reference numerals indicating each part changed to 2.

[0029] Each of the switching elements included in the above-described first AC / DC conversion circuit group 10 and second AC / DC conversion circuit group 20 may include a free wheel diode, as shown in Fig. 1. The switching of each of these switching elements is controlled by a control device 40. An IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor field-effect transistor) can be used as each switching element.

[0030] <Configuration of the conversion section> The conversion unit 30 is a circuit block whose main function is to convert voltage and transfer power between the first AC / DC conversion circuit 11 and the third AC / DC conversion circuit 21, and between the second AC / DC conversion circuit 12 and the fourth AC / DC conversion circuit 22.

[0031] 1 diagrammatically shows a first conversion unit 31 that is responsible for AC power transfer between the first AC / DC conversion circuit 11 and the third AC / DC conversion circuit 21, and includes an ideal transformer with a transformation ratio of N:1 (N is a winding ratio) and an inductance element L1 connected to the ideal transformer. Here, the transformation ratio is represented as N on the side of the first AC / DC conversion circuit 11. Such a first conversion unit 31 is disposed between the AC side terminal pair (terminal x11 and terminal y11) of the first AC / DC conversion circuit 11 and the AC side terminal pair (terminal x21 and terminal y21) of the third AC / DC conversion circuit 21.

[0032] Also shown is a schematic representation of a second conversion unit 32 that includes an ideal transformer with a transformation ratio of N:1 and an inductance element L2 connected to the ideal transformer and is responsible for AC power transfer between the second AC-DC conversion circuit 12 and the fourth AC-DC conversion circuit 22. Such a second conversion unit 32 is disposed between an AC side terminal pair (terminal x12 and terminal y12) of the second AC-DC conversion circuit 12 and an AC side terminal pair (terminal x22 and terminal y22) of the fourth AC-DC conversion circuit 22.

[0033] Therefore, each of the circuit in which the first AC / DC conversion circuit 11, the first conversion unit 31, and the third AC / DC conversion circuit 21 are connected, and the circuit in which the second AC / DC conversion circuit 12, the second conversion unit 32, and the fourth AC / DC conversion circuit 22 are connected has the functions of a typical isolated DC-DC converter unit.

[0034] However, in the DC-DC converter 1 according to the first embodiment, the isolation transformers of these two virtual isolated DC-DC converter units are not configured independently, but are configured as a transformer Tr in which each winding is wound around a common core 39. The multiple windings wound around the core 39 are made up of first windings connected to the AC side terminal pairs of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group 10, and second windings connected to the AC side terminal pairs of each of the AC-DC conversion circuits constituting the second AC-DC conversion circuit group 20.

[0035] Therefore, power can be transferred between the AC / DC conversion circuits. Fig. 2 is a conceptual diagram showing the transformer Tr of the conversion unit 30. The transformer Tr has four windings corresponding to the four AC / DC conversion circuits. The first winding, a winding W1, is connected to an AC side terminal pair (terminal x11 and terminal y11) of the first AC / DC conversion circuit 11. The first winding, a winding W2, is connected to an AC side terminal pair (terminal x12 and terminal y12) of the second AC / DC conversion circuit 12.

[0036] The winding W3, which is the second winding, is connected to an AC side terminal pair (terminal x21 and terminal y21) of the third AC / DC conversion circuit 21. The winding W4, which is the second winding, is connected to an AC side terminal pair (terminal x22 and terminal y22) of the fourth AC / DC conversion circuit 22. Note that reactors may be appropriately inserted between each of these windings and each terminal as actual elements that serve as part of the inductance components of the conversion unit 30, particularly the inductance elements L1 and L2 in FIG. 1 or 3.

[0037] Fig. 3 shows an equivalent circuit of the conversion unit 30 including the transformer Tr having four windings W1 to W4. The equivalent circuit in Fig. 3 equivalently represents the conversion unit 30 as a circuit described below. The equivalent circuit has four ideal transformers having windings W1 to W4 as one winding connected to the AC side terminal pairs of each AC / DC conversion circuit. The transformation ratio of the ideal transformers is 1:1 for each of the first AC / DC conversion circuit 11 and the second AC / DC conversion circuit 12, and N:1 for each of the third AC / DC conversion circuit 21 and the fourth AC / DC conversion circuit 22.

[0038] One terminal of each of the other windings (virtual windings) of each ideal transformer is connected to each other. These may be grounded as shown in the figure. The other terminals of the other windings are referred to as terminal A, terminal B, terminal C, and terminal D for the ideal transformers connected to the first AC / DC conversion circuit 11, the third AC / DC conversion circuit 21, the second AC / DC conversion circuit 12, and the fourth AC / DC conversion circuit 22, respectively.

[0039] The equivalent circuit in Fig. 3 has an inductance element L1 arranged between terminals A and B, and an inductance element L2 arranged between terminals C and D. These inductance elements are equivalent to the inductance elements L1 and L2 shown in Fig. 1, respectively. The equivalent circuit also has inductance elements Lac, Lbd, Lad, and Lbc arranged between terminals A and C, terminals B and D, terminals A and D, and terminals B and C, respectively. The symbols representing each inductance element are also used as symbols representing the inductance of each inductance element.

[0040] <On / off control of each switching element> The control device 40 controls the switching of each switching element by setting the switching phase of the first AC / DC conversion circuit 11, which is an AC / DC conversion circuit constituting the first AC / DC conversion circuit group 10, to the same as the switching phase of the second AC / DC conversion circuit 12. More preferably, the control device 40 controls the switching phase of the third AC / DC conversion circuit 21, which is an AC / DC conversion circuit constituting the second AC / DC conversion circuit group 20, to the same as the switching phase of the fourth AC / DC conversion circuit 22.

[0041] Here, for example, making the switching phase of the first AC / DC conversion circuit 11 and the switching phase of the second AC / DC conversion circuit 12 the same means the following: All of the switching elements in the first AC / DC conversion circuit 11 and the corresponding switching elements in the second AC / DC conversion circuit 12 are turned on and off in the same phase.

[0042] In each AC / DC converter circuit, a suitable known method may be applied to the method of controlling the switching of each switching element. The following is an example.

[0043] In each leg of the first AC / DC conversion circuit 11, the switching elements connected in series, for example, the switching elements S11 and S21, are controlled to invert on / off at an on-duty of 50% so that they are not simultaneously conductive. Alternatively, these switching elements may be controlled so that the on-duty is less than 50% with a switching phase difference of 180°. Also, the on / off timing may be adjusted taking into account the so-called dead time.

[0044] In general, switching element S11 (upper arm of one leg) and switching element S41 (lower arm of the other leg) are turned on / off in the same phase, and the same is true for switching element S21 and switching element S31. This state is defined as a phase difference between the legs being 0, and the control device 40 may perform such control to set the phase difference between the legs to 0, or may further perform control to appropriately adjust the phase difference between the legs to a value other than 0. Switching control is performed for the other AC / DC conversion circuits in the same manner as for the first AC / DC conversion circuit 11.

[0045] Furthermore, the control device 40 determines the inter-bridge phase difference, which is the phase difference in switching between the AC / DC conversion circuits constituting the first AC / DC conversion circuit group 10 and the AC / DC conversion circuits constituting the second AC / DC conversion circuit group 20, in accordance with the power transferred between the first DC voltage source and the second DC voltage source. If the inter-bridge phase difference is 0, no power transfer is performed, and if an inter-bridge phase difference occurs, the direction of power transfer is determined by the positive or negative side, and power transfer is performed in accordance with the magnitude of the phase difference. Thus, the control device 40 controls the inter-bridge phase difference in accordance with the transferred power.

[0046] Thus, according to the first embodiment, there is no need for complicated control such as controlling the phase of each AC / DC conversion circuit by feedback of the imbalance of the burden voltage. Furthermore, according to the first embodiment, there is no need to control switching so as to intentionally increase the loss in a specific AC / DC conversion circuit in order to balance the burden voltages.

[0047] <Outline of operation example> An operation example of the DC-DC converter 1 according to the embodiment 1 will be described in comparison with the DC-DC converter 1R of the comparative example 1. Fig. 4 is a diagram showing voltage and current waveforms at each part of the DC-DC converter 1 when this operation example is executed. The reason why the currents shown in Fig. 4 are generated will be described later.

[0048] The AC voltages Vac11, Vac12, Vac21, and Vac22 are voltages between the AC side terminal pairs of the first AC / DC conversion circuit 11, the second AC / DC conversion circuit 12, the third AC / DC conversion circuit 21, and the fourth AC / DC conversion circuit 22, respectively. The AC currents Iac11, Iac12, Iac21, and Iac22 are input / output currents of the AC side terminal pairs of the first AC / DC conversion circuit 11, the second AC / DC conversion circuit 12, the third AC / DC conversion circuit 21, and the fourth AC / DC conversion circuit 22, respectively. The inductor currents Iab, Iac, Iad, Ibc, Ibd, and Icd are currents flowing through the inductance elements L1, Lac, Lad, Lbc, Lbd, and L2 in the equivalent circuit of the conversion unit 30 in FIG. 3, respectively.

[0049] In this operation example, the control of the switching operation by the control device 40 is performed under the following conditions. The switching phase of the first AC / DC conversion circuit 11 is the same as the switching phase of the second AC / DC conversion circuit 12, and the switching phase of the third AC / DC conversion circuit 21 is the same as the switching phase of the fourth AC / DC conversion circuit 22. In addition, the phase difference between the bridges is set to 0 so that the power transfer between the first DC voltage source 91 and the second DC voltage source 92 is 0. The phase difference between the legs in each AC / DC conversion circuit is 0. The transformation ratio N is set to 1.25.

[0050] <Configuration of DC-DC Converter in Comparative Example 1> 5 is a diagram showing a circuit configuration of a DC-DC converter 1R of Comparative Example 1, which is a comparative example related to the DC-DC converter 1. The DC-DC converter 1R of Comparative Example 1 has a configuration similar to the prior art, in which an isolated DC-DC converter unit 1R1 and an isolated DC-DC converter unit 1R2 are configured as isolated DC-DC converter units independent of each other.

[0051] The transformer Tr1 of the isolated DC-DC converter unit 1R1 in Comparative Example 1 and the transformer Tr2 of the isolated DC-DC converter unit 1R2 are separate transformers and do not share a core as in Embodiment 1. The control device 1R4 in the DC-DC converter 1R in Comparative Example 1 controls the switching of each switching element in the same manner as the control for the corresponding switching element in the DC-DC converter 1 according to Embodiment 1.

[0052] In Comparative Example 1, it was assumed that there was variation in the iron loss of the transformer between the isolated DC-DC converter unit 1R1 and the isolated DC-DC converter unit 1R2, and also in the characteristics of the capacitor of the smoothing circuit. The same variation was also assumed in the DC-DC converter 1 according to the first embodiment.

[0053] <Comparison of operation examples> Fig. 6 is a graph showing the DC voltages of the AC / DC conversion circuits during operation of the DC-DC converter 1R of Comparative Example 1, and illustrates the states before and after switching of each switching element under the control of the control device 40 is started at time 0. The horizontal axis represents time in arbitrary units. Fig. 7 is a similar graph showing the DC voltages of the AC / DC conversion circuits during operation of the DC-DC converter 1R according to embodiment 1.

[0054] In Figures 6 and 7, the difference between DC voltages Vdc11 and Vdc12 and the difference between DC voltages Vdc21 and Vdc22 before switching begins are caused by variations in the characteristics of the capacitors in the smoothing circuits of each AC / DC conversion circuit.

[0055] After the switching operation is started, the DC voltages become constant after a while, but in the DC-DC converter 1R of Comparative Example 1, the DC voltages vary and the voltage burden is uneven on both the first DC voltage source 91 side (first terminal side) and the second DC voltage source 92 side (second terminal side). On the other hand, it was found that the DC-DC converter 1 according to Embodiment 1 operates so that the voltage burden of each AC-DC conversion circuit is uniform on both the first DC voltage source 91 side (first terminal side) and the second DC voltage source 92 side (second terminal side).

[0056] <effect> The reason why the circuit configuration of the DC-DC converter 1 according to the first embodiment realizes a balance of the voltages borne by each AC-DC conversion circuit will be described below. For example, when the DC voltage Vdc11 applied to the capacitor C11 becomes higher than the DC voltages applied to the other capacitors, the following sequence is performed to suppress the voltage difference. Note that the magnitude of the DC voltages between the capacitors is compared using converted voltages that take into account the transformation ratio of the transformer Tr of the conversion unit 30.

[0057] When a voltage difference occurs between the DC voltage Vdc11 of capacitor C11 and the DC voltages Vdc21, Vdc12, and Vdc22 of the other capacitors, a circulating current is generated that charges and discharges between capacitor C11 and the other capacitors. This causes losses such as conduction loss in the switching elements and copper loss in the transformer Tr. The current equivalent to this loss is discharged from capacitor C11 and charged to the other low-voltage side capacitors.

[0058] The circulating current reduces the voltage difference between the DC voltage Vdc11 of the capacitor C11 and the DC voltages Vdc21, Vdc12, and Vdc22 of the other capacitors, and the circulating current decreases over time. Thus, on the first DC voltage source 91 side, the difference between the DC voltage Vdc11 of the capacitor C11 and the DC voltage Vdc12 of the capacitor C12 is suppressed. Also, on the second DC voltage source 92 side, the difference between the DC voltage Vdc21 of the capacitor C21 and the DC voltage Vdc22 of the capacitor C22 is suppressed.

[0059] For example, the AC current Iac11 input / output to / from the AC side terminal pair (terminal x11 and terminal y11) of the first AC / DC conversion circuit 11 is expressed by the following equation at time t within a quarter cycle before and after the current becomes 0: Iac11=Iab+Iac+Iad=(Vac11-N·Vac21)t / L1+(Vac11-Vac12)t / Lac+(Vac11-N·Vac22)t / Lad.

[0060] In addition, the smaller the inductance of the inductance elements Lac, Lad, Lbc, and Lbd, the larger the circulating current becomes, and the greater the effect of suppressing the voltage difference becomes. The inductance of the inductance elements L1 and L2 is determined taking into consideration the rated power. In addition, in each AC / DC conversion circuit group, the greater the number of AC / DC conversion circuits connected in series, the greater the number of paths for the circulating current becomes, and the greater the effect of suppressing the voltage difference becomes.

[0061] 8 is a circuit diagram in which arrows indicate return currents that occur when an imbalance occurs in which the voltage on the DC voltage Vdc11 side is higher, focusing on the DC voltages Vdc11 and Vdc12 on the first DC voltage source 91 side (first terminal side) in the DC-DC converter 1. In FIG. 8, the control device 40 is omitted, and the conversion unit 30 is represented by the equivalent circuit in FIG.

[0062] 8 shows a state at a timing when the switching elements S11 and S41 are on and the switching elements S21 and S31 are off in the first AC-DC conversion circuit 11. As described above, the switching phase of the second AC-DC conversion circuit 12 is the same as that of the first AC-DC conversion circuit 11.

[0063] In the circuit configuration of the DC-DC converter 1, the capacitor C11 of the first AC-DC conversion circuit 11 and the capacitor C12 of the second AC-DC conversion circuit 12 are connected by a return current path shown by the arrow in the figure that passes through the inductance element Lac in the equivalent circuit. Therefore, for example, when the DC voltage Vdc11 that is the voltage applied to the capacitor C11 is greater than the DC voltage Vdc12 that is the voltage applied to the capacitor C12, a return current in the direction of the arrow that moves charge so that the capacitor C11 charges the capacitor C12 flows as a compensation current that compensates for the voltage difference.

[0064] At the timing when the on / off state of the switching element is reversed from the state shown in Fig. 8, the increase and decrease of the current flowing through conversion unit 30 is reversed. The direction of the current flowing through the ideal transformer and inductance element Lac of the equivalent circuit of conversion unit 30 in the return current path shown in Fig. 8 alternates, and the compensation current flows as an AC current through these circuit elements. In capacitors C11 and C12, a current that charges capacitor C11 and capacitor C12 on a time average flows as the compensation current.

[0065] In the circuit configuration of the DC-DC converter 1, the AC-DC conversion circuits constituting the first AC-DC conversion circuit group 10 are electromagnetically coupled to each other in the conversion unit 30 by the transformer Tr and are not independent, so that such a compensation current can flow. Therefore, according to the DC-DC converter 1 of the first embodiment, as shown in the result of Fig. 7, the voltages borne by each AC-DC conversion circuit on the first DC voltage source 91 side (first terminal side) and the second DC voltage source 92 side (second terminal side) are well balanced.

[0066] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0067] 9 is a circuit diagram showing the configuration of a DC-DC converter 2 according to embodiment 2. In the DC-DC converter 2, the DC side terminal pair (terminals u21 and v21) of the third AC-DC conversion circuit 21 and the DC side terminal pair (terminals u22 and v22) of the fourth AC-DC conversion circuit 22 are connected in parallel to the second terminal pair (terminals u2 and v2). The other configurations are the same as those of the DC-DC converter 1 according to embodiment 1.

[0068] Thus, in the DC-DC converter 2, the third AC-DC conversion circuit 21 and the fourth AC-DC conversion circuit 22 are connected in parallel to the second DC voltage source 92. Therefore, in the second AC-DC conversion circuit group 20, the third AC-DC conversion circuit 21 and the fourth AC-DC conversion circuit 22 share the input / output current to / from the second DC voltage source 92, thereby distributing the power burden.

[0069] The connection of each terminal to the second terminal pair will be described in detail as follows. The high potential side terminal u2 of the second terminal pair is electrically common to the high potential side terminal u21 of the DC side terminal pair of the third AC / DC conversion circuit 21 and the high potential side terminal u22 of the DC side terminal pair of the fourth AC / DC conversion circuit 22. The low potential side terminal v2 of the second terminal pair is electrically common to the low potential side terminal v21 of the DC side terminal pair of the third AC / DC conversion circuit 21 and the low potential side terminal v22 of the DC side terminal pair of the fourth AC / DC conversion circuit 22.

[0070] 10 is a diagram showing a comparison of an operation example of the DC-DC converter 2 according to the embodiment 2 and a DC-DC converter of Comparative Example 2. Comparative Example 2 is a DC-DC converter having a similar configuration to the DC-DC converter 1R of Comparative Example 1, except that the interconnections of the DC side terminal pair of the third AC-DC conversion circuit 21, the DC side terminal pair of the fourth AC-DC conversion circuit 22, and the second terminal pair are changed in the same way as in the DC-DC converter 2.

[0071] 10, an inter-bridge phase was provided to transfer power from first DC voltage source 91 to second DC voltage source 92, and other than this, switching control of each switching element was performed in the same manner as in embodiment 1. Note that switching control of each switching element was started at the left end of each graph.

[0072] Thus, Fig. 10 shows the result of powering operation when the AC / DC conversion circuits are connected in series on the input side and in parallel on the output side. In Fig. 10, DC voltages Vdc11 and Vdc12 are shown to show the balance of voltages on the input side. In addition, DC current Idc21, which is the terminal current of the DC side terminal pair of the third AC / DC conversion circuit 21, and DC current Idc22, which is the terminal current of the DC side terminal pair of the fourth AC / DC conversion circuit 22, are shown to show the balance of currents on the output side.

[0073] 10, it is clear that the DC-DC converter 2 according to the second embodiment operates to balance the DC voltage Vdc11 and the DC voltage Vdc12, as compared with the comparative example 2. This is because, as in the description of the first embodiment, the first AC-DC conversion circuit group 10 acts to balance the voltages of the AC-DC conversion circuits.

[0074] As a result, the transfer power shared by each AC / DC conversion circuit in the first AC / DC conversion circuit group 10 is balanced, and the transfer power shared by each AC / DC conversion circuit in the second AC / DC conversion circuit group 20 is also balanced. Thus, the variation in input / output current for each AC / DC conversion circuit in the second AC / DC conversion circuit group 20 is also reduced compared to Comparative Example 2. The result in Fig. 10 is synonymous with the result of regenerative operation when AC / DC conversion circuits are connected in parallel on the input side and AC / DC conversion circuits are connected in series on the output side.

[0075] [Embodiment 3] 11 is a circuit diagram showing the configuration of a DC-DC converter 3 according to embodiment 3. In the DC-DC converter 3, the DC side terminal pair (terminals u11 and v11) of the first AC-DC conversion circuit 11 and the DC side terminal pair (terminals u12 and v12) of the second AC-DC conversion circuit 12 are connected in parallel to the first terminal pair (terminals u2 and v2). The other configurations are the same as those of the DC-DC converter 1 according to embodiment 1.

[0076] In this manner, in the DC-DC converter 3, the first AC-DC conversion circuit 11 and the second AC-DC conversion circuit 12 are connected in parallel to the first DC voltage source 91. Therefore, in the first AC-DC conversion circuit group 10, the first AC-DC conversion circuit 11 and the second AC-DC conversion circuit 12 share the input / output current to / from the first DC voltage source 91, thereby distributing the power burden.

[0077] The connection of each terminal to the first terminal pair will be described in detail as follows. The high potential side terminal u1 of the first terminal pair is electrically common to the high potential side terminal u11 of the DC side terminal pair of the first AC / DC conversion circuit 11 and the high potential side terminal u12 of the DC side terminal pair of the second AC / DC conversion circuit 12. The low potential side terminal v1 of the first terminal pair is electrically common to the low potential side terminal v11 of the DC side terminal pair of the first AC / DC conversion circuit 11 and the low potential side terminal v12 of the DC side terminal pair of the second AC / DC conversion circuit 12.

[0078] 12 is a diagram showing a comparison of an operation example of the DC-DC converter 3 according to the embodiment 3 and a DC-DC converter of Comparative Example 3. Comparative Example 3 is a DC-DC converter having a similar configuration to the DC-DC converter 1R of Comparative Example 1, except that the mutual connections of the DC side terminal pair of the first AC-DC conversion circuit 11, the DC side terminal pair of the second AC-DC conversion circuit 12, and the first terminal pair are changed in the same way as in the DC-DC converter 3.

[0079] 12, an inter-bridge phase was provided to transfer power from first DC voltage source 91 to second DC voltage source 92, and other than this, switching control of each switching element was performed in the same manner as in embodiment 1. Note that switching control of each switching element was started at the left end of each graph.

[0080] Thus, Fig. 12 shows the result of powering operation when the AC / DC conversion circuits are connected in parallel on the input side and in series on the output side. In Fig. 12, DC voltages Vdc21 and Vdc22 are shown to show the balance of voltages on the output side. In addition, DC current Idc11, which is the terminal current of the DC side terminal pair of the first AC / DC conversion circuit 11, and DC current Idc12, which is the terminal current of the DC side terminal pair of the second AC / DC conversion circuit 12, are shown to show the balance of currents on the input side.

[0081] 12, it is clear that the DC-DC converter 3 according to the third embodiment operates to balance the DC voltage Vdc21 and the DC voltage Vdc22, as compared with the comparative example 3. This is because, as in the description of the first embodiment, the compensation current in the second AC / DC conversion circuit group 20 acts to balance the voltages of the AC / DC conversion circuits.

[0082] As a result, the transfer power shared by each AC / DC conversion circuit in the second AC / DC conversion circuit group 20 is balanced, and the transfer power shared by each AC / DC conversion circuit in the first AC / DC conversion circuit group 10 is also balanced. Thus, the variation in input / output current for each AC / DC conversion circuit in the first AC / DC conversion circuit group 10 is also reduced compared to Comparative Example 3. The result in Fig. 12 is synonymous with the result of regenerative operation when the AC / DC conversion circuits are connected in series on the input side and the AC / DC conversion circuits are connected in parallel on the output side.

[0083] 〔summary〕 A first aspect of the present disclosure is a DC-DC converter including a first terminal pair and a second terminal pair, and controlling a transfer of power between the first terminal pair and the second terminal pair, the DC-DC converter including a first AC-DC conversion circuit group including a plurality of AC-DC conversion circuits, each including a smoothing circuit and an active bridge circuit connected in cascade from the first terminal pair, and provided with an AC side terminal pair connected to the active bridge circuit for inputting and outputting AC power, and a first winding connected to the AC side terminal pair of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, each including a smoothing circuit and an active bridge circuit connected in cascade from the second terminal pair, the active bridge circuit including a first winding connected to the AC side terminal pair of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, and a smoothing circuit and an active bridge circuit connected in cascade from the second terminal pair, the active bridge circuit including a first winding connected to the AC side terminal pair of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, the active bridge circuit including a first winding connected to the AC side terminal pair of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, and the active bridge circuit including a first winding connected to the AC side terminal pair of each of the AC-DC conversion circuits constituting the first AC-DC conversion circuit group, ... a second AC / DC conversion circuit group constituted by at least one AC / DC conversion circuit having an AC side terminal pair for inputting and outputting AC power connected to a first bias circuit; a second winding connected to the AC side terminal pair of each of the AC / DC conversion circuits constituting the second AC / DC conversion circuit group, a core, and a control unit that controls switching elements included in the first AC / DC conversion circuit group, wherein the DC side terminal pairs for inputting and outputting DC power of the AC / DC conversion circuits constituting the first AC / DC conversion circuit group are connected in series between the first terminal pair, and a transformer is constituted in which the first winding and the second winding are commonly wound around the core.

[0084] A DC-DC converter according to a second aspect of the present disclosure is related to the first aspect, and further includes a configuration in which the control unit performs switching of the respective AC / DC conversion circuits constituting the first group of AC / DC conversion circuits in the same phase.

[0085] A DC-DC converter according to aspect 3 of the present disclosure is configured in such a manner that, in accordance with aspect 2 above, the control unit determines a switching phase difference of the AC-DC conversion circuits constituting the second AC-DC conversion circuit group relative to the AC-DC conversion circuits constituting the first AC-DC conversion circuit group in accordance with the power transferred between the first terminal pair and the second terminal pair.

[0086] A DC-DC converter according to aspect 4 of the present disclosure is configured in any one of aspects 1 to 3 above, such that the second AC / DC conversion circuit group is composed of a plurality of the AC / DC conversion circuits, and DC side terminal pairs of the AC / DC conversion circuits for inputting and outputting DC power are connected in series between the second terminal pairs.

[0087] A DC-DC converter according to a fifth aspect of the present disclosure is related to the fourth aspect, and further includes a configuration in which the control unit performs switching of the respective AC / DC conversion circuits constituting the second group of AC / DC conversion circuits in the same phase.

[0088] A DC-DC converter according to aspect 6 of the present disclosure is any one of aspects 1 to 5 above, wherein the second group of AC-DC conversion circuits is composed of a plurality of the AC-DC conversion circuits, and DC side terminal pairs of the AC-DC conversion circuits for inputting and outputting DC power are connected in parallel to the second terminal pair.

[0089] [Software implementation example] The functions of the control device 40 (hereinafter referred to as the "device") can be realized by a program for making a computer function as the device. In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The functions described in each of the above embodiments are realized by executing the program using the control device and the storage device.

[0090] The program may be recorded non-transiently on one or more computer-readable recording media. The device may or may not have the recording media. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium. In addition, some or all of the functions of the device may be realized by a logic circuit. For example, an integrated circuit in which a logic circuit that functions as the device is formed is also included in the scope of the present invention.

[0091] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0092] For example, in the first embodiment, a configuration in which two AC / DC conversion circuits are connected in series on the second DC voltage source 92 side is exemplified, but three or more AC / DC conversion circuits may be connected in series. Alternatively, one AC / DC conversion circuit may be connected to the second DC voltage source 92. In the second embodiment, a configuration in which two AC / DC conversion circuits are connected in parallel on the second DC voltage source 92 side is exemplified, but three or more AC / DC conversion circuits may be connected in parallel. [Explanation of symbols]

[0093] 1, 2, 3 DC-DC Converter (u1, v1) 1st terminal pair (u2, v2) Second terminal pair 10 First AC / DC conversion circuit group 11 First AC / DC converter circuit 12 Second AC / DC conversion circuit (u11, v11), (u12, v12) DC side terminal pair (x11, y11), (x12, y12) AC side terminal pair 20 Second AC / DC conversion circuit group 21 Third AC / DC converter circuit 22 4th AC / DC converter circuit (u21, v21), (u22, v22) DC side terminal pair (x21, y21), (x22, y22) AC side terminal pair 111, 121, 211, 221 smoothing circuit 112, 122, 212, 222 Active bridge circuit 30 Conversion unit 31 First conversion unit 32 Second conversion section Tr Transformer 39 cores W1, W2 Winding (1st Winding) W3, W4 winding (second winding) 40 Control device (control unit) 91 First DC voltage source 92 Second DC voltage source

Claims

1. A DC-DC converter comprising a first terminal pair and a second terminal pair, the DC-DC converter controlling a transfer of power between the first terminal pair and the second terminal pair, a first AC / DC conversion circuit group including a plurality of AC / DC conversion circuits, each of which includes a smoothing circuit and an active bridge circuit cascade-connected from the first terminal pair side, and is provided with an AC side terminal pair connected to the active bridge circuit for inputting and outputting AC power; a first winding connected to the AC side terminal pairs of each of the AC / DC conversion circuits constituting the first group of AC / DC conversion circuits; a second AC / DC conversion circuit group including at least one AC / DC conversion circuit, each of which includes a smoothing circuit and an active bridge circuit cascade-connected from the second terminal pair side, and is provided with an AC side terminal pair connected to the active bridge circuit for inputting and outputting AC power; a second winding connected to the AC side terminal pairs of each of the AC / DC conversion circuits constituting the second AC / DC conversion circuit group; A core, a control unit that controls switching elements included in the first group of AC / DC conversion circuits and the second group of AC / DC conversion circuits, a DC side terminal pair for inputting and outputting DC power of the AC / DC conversion circuit constituting the first AC / DC conversion circuit group is connected in series between the first terminal pair, a transformer is configured in which the first winding and the second winding are commonly wound around the core, The control unit is A DC-DC converter that performs switching of each of the AC-DC conversion circuits that constitute the first AC-DC conversion circuit group in the same phase, and further determines a phase difference of switching of the AC-DC conversion circuits that constitute the second AC-DC conversion circuit group relative to the AC-DC conversion circuits that constitute the first AC-DC conversion circuit group in accordance with power transferred between the first terminal pair and the second terminal pair.

2. The DC-DC converter according to claim 1, wherein the second AC-DC conversion circuit group is composed of a plurality of the AC-DC conversion circuits, and DC side terminal pairs of the AC-DC conversion circuits for inputting and outputting DC power are connected in series between the second terminal pairs.

3. The control unit is 3. The DC-DC converter according to claim 2, wherein switching of each of the AC-DC conversion circuits constituting the second group of AC-DC conversion circuits is performed in the same phase.

4. The DC-DC converter according to claim 1, wherein the second AC-DC conversion circuit group is composed of a plurality of the AC-DC conversion circuits, and DC side terminal pairs of the AC-DC conversion circuits for inputting and outputting DC power are connected in parallel to the second terminal pairs.

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